1. Field of the Invention
The present invention relates to video imagery, and, in particular, to methods and apparatuses for generating CLUT-format video images from three-component video data.
2. Description of the Related Art
It is desirable to display real-time motion video on personal computer (PC) systems. In conventional digital video systems, each picture element (i.e., pixel or pel) of a video image is represented by three multi-bit values. For example, in YUV-format systems, each pixel is represented by three 8-bit parameters Y, U, and V. The values of Y, U, and V for a pixel correspond to the color of the pixel.
Theoretically, since each 8-bit parameter Y, U, and V can have 2.sup.8 or 256 different values, there are 2.sup.24 or 16,777,216 possible combinations of Y, U, and V in YUV format. Most of these combinations, however, either do not correspond to real colors or are not needed to satisfy typical fidelity requirements for video imagery.
To display video images on PC systems, the YUV data for each pixel may be converted to a color look-up table (CLUT) index value. The CLUT is a palette that contains a defined set of colors for display on the PC system. For example, a CLUT may contain 2.sup.8 or 256 different colors. Since video imagery in YUV format typically contains more than 256 different colors, converting the three 8-bit YUV image data to single 8-bit CLUT index values involves selecting CLUT colors that are "close" to the actual YUV colors.
When displaying video imagery on PC systems having a limited number of CLUT palette colors, color fidelity may be improved by dithering. Dithering involves the "mixing" at the pixel-to-pixel level of different colors from the CLUT palette to give the subjective look of a color closer to the actual YUV color.
It is also desirable, in a PC system for displaying real-time motion video, to store the video data efficiently and to process and display the data sufficiently fast to present the look of real-time motion. To reduce data storage requirements, digital video image data may be stored in a subsampled format. For example, in YUV-9 format, each four-pixel-by-four-pixel subimage of each video image is represented by sixteen 8-bit Y values (i.e., one Y value for each of the sixteen pixels in the subimage), only one 8-bit U value, and only one 8-bit V value. Similarly, in YUV-12 format, each two-pixel-by-two-pixel subimage is represented by four Y values, one U value, and one V value.
It is therefore an object of the present invention to provide methods and apparatuses for generating CLUT-format video images on PC systems.
It is another object of the present invention to convert three-component video data into CLUT format.
It is another object of the present invention to generate dithered video images.
It is another object of the present invention to generate CLUT-format video images from subsampled video data.
It is a specific object of the present invention to convert subsampled video data in YUV-9 or YUV-12 format to full-resolution, dithered, CLUT-format video data with sufficient speed and quality to display real-time motion video on PC systems.
Further objects of this invention will become apparent from the detailed description of a preferred embodiment which follows.